I. Field
The present disclosure relates generally to wireless communications and more specifically to frequency tracking.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content such as, for example, voice, data, and so on. Typical wireless communication systems may be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, . . . ). Examples of such multiple-access systems may include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. Additionally, the systems can conform to specifications such as third generation partnership project (3GPP), 3GPP long term evolution (LTE), ultra mobile broadband (UMB), and/or multi-carrier wireless specifications such as evolution data optimized (EV-DO), one or more revisions thereof, etc., which can utilize evolved universal terrestrial radio access (E-UTRA) to facilitate radio communication between wireless devices. E-UTRA can also be utilized in evolved packet systems (EPS), such as 3GPP LTE.
Generally, wireless multiple-access communication systems may simultaneously support communication for multiple mobile devices. Each mobile device may communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to base stations. Further, communications between mobile devices and base stations may be established via single-input single-output (SISO) systems, multiple-input single-output (MISO) systems, multiple-input multiple-output (MIMO) systems, and so forth. In addition, mobile devices can communicate with other mobile devices (and/or base stations with other base stations) in peer-to-peer wireless network configurations.
Receivers utilized for wireless communications, however, can experience frequency error over time. This frequency error can cause reduced signal amplitude, phase offset, and inter-carrier interference (e.g., in an orthogonal frequency division multiplexing (OFDM) system), etc., since the full signal is not properly received. Previous solutions to this issue include pilot signal aided frequency estimation where adjacent time segments of OFDM waveforms, which include pilot signals, can be used for frequency estimations to align the receiver frequency. In addition, cyclic prefix (CP)-based frequency estimation can be utilized to account for the error where portions of transmissions are repeated within the transmission and the repeated portions can be used to estimate frequency error. Since CP repeats the transmission within the original transmission resources, the effective allowable time for transmissions decreases, which in turn decreases the system capacity.
In addition, timing tracking loops exist that correct timing of wireless devices for synchronization with disparate devices. Timing tracking loops typically determine a timing tracking discriminator signal by subtracting an early shift in time domain of a received pilot sequence from a late shift in time domain of the received pilot sequence. The discriminator signal can be utilized to estimate timing error in the device by multiplying a gain signal, summing a feedback signal, and detecting overflow/underflow in the resulting signal. Where values of the resulting signal are in a predetermined range, there is no need to correct the device for timing error. Where values of the resulting signals overflow the range, however, the device can advance timing related to the overflow amount. Similarly, where values of the resulting signals underflow the range, the device can reduce timing according to the underflow.